In many fields of technology, use is made of circuits integrated in a semiconductor material for the purpose of reading out and processing measuring signals that originate from a sensor assigned to the integrated circuit. Such combinations of sensors and integrated circuits are to be found, for example, in X-ray detectors of X-ray computed tomography units. The X-ray detectors are generally constructed from a multiplicity of juxtaposed detector modules of which each comprises a sensor for X-radiation and an integrated circuit connected to the sensor.
Components of the integrated circuit, such as capacitors, resistors, transistors or, inter alia, comparators or integrators constructed from transistors, in this case exhibit an operating behavior dependent on temperature, and this has an effect on the processing of the measuring signals obtained with the sensor. The stability of offset signals or the quality of the linearity of a circuit component may be named by way of example.
Again, the measurement response of the sensors for x-radiation is itself influenced by the temperature. If, for example, semiconductor-based photodiodes are used in the sensor, a doubling of the dark current of the photodiodes can be observed in each case in the event of an increase in the temperature of the semiconductor material from 5 to 9 kelvins. Thus, since the measuring accuracy of a detector module, in particular of its sensor for X-radiation and of its integrated circuit, depends on the temperature in a way that cannot be neglected, measures are taken in order at least to keep the sensor and the integrated circuit of a detector module substantially at a constant temperature.
Thus, US 2003/0168605 A1 discloses a radiation detector that has a device with the aid of which the radiation detector can be kept substantially at a constant temperature. The actual temperature of a semiconductor component of the detector is compared with the setpoint temperature via a comparator. In the event of a deviation from the setpoint temperature, heating resistors are supplied with current in order to heat the detector up to the setpoint temperature.
DE 196 15 178 C2 describes a device for digital radiography with a sensor device which includes a semiconductor sensor array, to which a scintillator layer is applied, that has a temperature control device for keeping the sensor device at a constant temperature. The sensor is preferably designed as a CCD sensor and provided on its rear side with a heating element, it being possible to keep the temperature of the sensor constant by active control.
DE 100 34 262 C1 discloses a circuit integrated in a semiconductor material and having an active component, a temperature sensor and a circuit. If the temperature measured by the temperature sensor undershoots a temperature limit value, the circuit causes a heat generating process. In this case, either dummy operating cycles of the circuit are initiated, or an oscillator which is provided separately is operated.
U.S. Pat. No. 5,517,052 A discloses a circuit that is integrated in a semiconductor material and has an active component, a temperature sensor and a circuit for controlling the temperature of the semiconductor material. The active component is “oscillating transistors”. The transistors use various heating elements in order to control the temperature.
WO 95/30200 A1 discloses a circuit integrated in a semiconductor material and having an active component that is a computer CPU. In order to control the CPU temperature acquired by a temperature sensor, a circuit is provided that varies the CPU clock rate in accordance with the acquired temperature, the generation of heat, and thus the CPU temperature, being influenced thereby.
DE 101 38 913 A1 relates to a detector module for an X-ray computer tomograph. A circuit that is not integrated in a semiconductor material is provided for measuring signals of a sensor assigned to the circuit. A separate heating element is provided for controlling the temperature of the semiconductor material.